Scanning probe microscopies applied to the study of the domain wall in a ferroelectric crystal.

Scanning near-field optical microscopy is capable of measuring the topography and optical signals at the same time. This fact makes this technique a valuable tool in the study of materials at nanometric scale and, in particular, of ferroelectric materials, as it permits the study of their domains structure without the need of chemical etching and, therefore, not damaging the surface (as will be demonstrated later). We have measured the scanning near-field optical microscopy transmission, as well as the topography, of an RbTiOPO(4) single crystalline slab, which exhibits two different of macroscopic ferroelectric domains. A chemical selective etching has been performed to distinguish between them, obtaining areas with a noticeable roughness (C(-) domain) in comparison with the original flat aspect of the other ones (C(+) domain). The effects of the selective chemical etching have been quantified in topographic images obtained by means of our fibre tip probe, and have been compared to topographic images obtained by Atomic Force Microscopy, with a better resolution. The near-field optical transmission images recorded have been obtained under different excitation wavelengths. These images are modulated by the light scattering due to the grains at the rough surface, which depends on the excitation wavelength used. In addition, they show a significant optical contrast due to the variations of the dielectric constant on the proximity of the ferroelectric domain wall.